The present invention relates generally to dimensionally stable, rigid polyurethane/polyisocyanurate foams and to polyol blends used to make such foams. Particularly, the present invention relates to polyol blends containing a polyether polyol blend, a polyester polyol, and hydrocarbon blowing agent.
Hydrocarbons are being employed in greater numbers as viable alternative blowing agents in the manufacture of rigid polyurethane or polyisocyanurate foams.
Due to the non-polar hydrophobic characteristics of hydrocarbons, they are only partially soluble in many polyols used to manufacture rigid polyurethane or polyisocyanurate foams. As a result of the poor solubility of hydrocarbon blowing agents, the blowing agent must usually be added to the polyol just prior to dispersing through a mix head. The limited shelf life of hydrocarbon-polyol mixtures has limited the ability of storing batches for later use.
Additional to the limited storage time for batches, is the potential limited process phase stability or limited resistance to separation into layers of different composition. If there is a phase separation during the process, often there may be non-uniform and uneven cell structures in the resultant polyurethane or polyisocyanurate foam. Such non-stable cell structure can lead to variations in the properties of a foam product, such as, the thermal conductivity which generally increases as a result of poor cell structure. Conversely, the R-factor, or insulative factor tends to decrease as a result of poor cell structure. Such a decrease in the R-factor would not be desirable in an application where the foam is to be used as an insulator, such as, for example, in a refrigerator door.
There is provided a phase stable polyol resin blend composition comprising a polyether polyol blend, a polyester polyol and a hydrocarbon blowing agent. The polyether polyol blend is present in an amount of at least 10 percent by weight of the polyol resin.
In one embodiment, the polyether polyol blend comprises a mixture of a toluene diamine and ethylene diamine co-initiated polyol having from 20 to 30 percent ethylene oxide and 70 to 80 percent propylene oxide, a sucrose and dipropylene glycol co-initiated propylene oxide polyol, and a polyethylene terephthalate initiated aromatic polyol blend having a functionality of between 2.3 and 3.0
In one embodiment, the polyester polyol utilized in the invention is a phthalic anhydride initiated polyester polyol having a hydroxyl number of at least 200 meq polyol/g KOH.
The hydrocarbon blowing agents used by the invention are C4-C6 hydrocarbons or mixtures thereof. The pentanes are particularly preferred and are present in the polyol resin in amounts of from 20 to 30 parts by weight of the polyol resin.
In one embodiment, the method of the invention comprises providing a polyether polyol blend having at least three polyols comprising a toluene diamine and ethylene diamine co-initiated polyol, a sucrose and dipropylene glycol co-initiated polyol and a polyethylene terephthalate initiated aromatic polyol blend; providing a polyester polyol; providing a C4-C6 hydrocarbon blowing agent; combining the polyether polyol blend, polyester polyol and blowing agent to form a polyol resin; providing a polyisocyanate component; providing a catalyst; and combining the polyol resin with the polyisocyanate component and catalyst to form a polyurethane foam.